Process and apparatus for improving the transfer of heat from a hot gaseous fluid



Sept. 27, 1966 J. HUYGHE ET AL 3,274,752

PROCESS AND APPARATUS FOR IMPROVING THE TRANSFER OF HEAT FROM A HOT GASEOUS FLUID Filed Jan. 28, 1963 United States Patent 3,274,752 PROCESS AND APPARATUS FOR IMPROVING THE TRANSFER OF HEAT FROM A HOT GASEOUS FLUID Jean Huyghe and Henri Mondin, Grenoble, France, as-

signors to Commissariat a lEnergie Atomique, Paris, France Filed Jan. 28, 1963, Ser. No. 254,142 Claims priority, application France, Feb. 13, 1962, 887,885 8 Claims. (Cl. 55-89) The present invention relates to an improvement in heatexchangers and more particularly to a method for improving t-he transfer of heat from one fluid to another: the cooling fluid may be liquid or gaseous and the fluid giving up heat is gaseous.

The invention also relates to a device for the application of the said method, and to heat-exchangers of all types, so designed as to allow the application of the said method.

The fact that to mix a small quantity of liquid with a gas used as cooler in a generator of heat energy greatly improves the coefficient of thermal exchange of the gas, is already known. However, this method always involves a considerable vaporisation of the injected liquid, from which various disadvantages result. For besides the limitation of the possible choice of the liquid, the considerable increase in the loss of load, and thus of pumping power, as a result of the increase in the quantity delivered, must be taken into account. This supplementary consumption of energy causes the loss of a by no means negligible fraction of the advantage gained in the heatexchange, and very greatly prejudices the thermodynamic rating and the yield of the installation. Lastly, in the foregoing case, difliculties arising from the search for a convenient method of separating the auxiliary fluid or liquid and the principal gaseous fluid must also be taken into consideration.

The object of the present invention is to remedy or at least minimise these disadvantages by effecting not only a marked improvement in the heat-exchanges, but also providing a simpler construction of the exchangers, ensuring a worthwhile improvement in their performances without thereby increasing their cost.

To this end, the invention provides a method for improving the transfer of heat from one fluid to another in a heat-exchanger, the cooling fluid being liquid or gaseous, and the fluid giving up the heat being gaseous, which consists in introducing an auxiliary liquid, which does not vaporise under working conditions, into the gaseous stream of hot fluid on its entry into the exchanger, and separating the gaseous phase from the liquid phase at the outlet from the exchanger.

The invention also provides a heat-exchanger for carrying out this method, and comprising a bundle of tubes inside which the hot Ifluid circulates, the said tubes being in contact through their outer surface with a cooling fluid, wherein a distribution chamber is located in the neighborhood of the end of the said bundle of tubes through which the said hot fluid enters the exchanger, through which chamber the said tubes pass and which is supplied with an adjustable quantity of auxiliary liquid by an adjustable delivery pump and injection elements to introduce a pre-determined quantity of the said auxiliary liquid into the said tubes, the said auxiliary liquid mixing with the said hot fluid, and wherein an element designed to allow the separation of the said auxiliary liquid and the said hot fluid, is provided in the neighborhood of the end of the bundle of tubes through which the said fluid leaves the exchanger.

3 ,274,752 Patented Sept. 27, 1956 ice In the drawings:

FIG. 1 is a diagrammatic view of the present heat exchanger; and

FIG. 2 is an enlarged horizontal, sectional view taken on line 22 of FIG. 1.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings, which show a heat-exchanger having a straight bundle of tubes, and built in accordance with the invention.

As will be seen in the drawings, the heat-exchanger under consideration has a bundle of straight tubes in which a gaseous fluid circulates which is to give up its heat to a second fluid or cooling fluid.

The hot gas enters the exchanger through a supply pipe 1, then circulatesin the bundle of tubes 2 along a path indicated by the arrows a, and is then evacuated by an exit pipe 3. The cooling liquid circulates in a conventional manner, in counterfiow, in the direction of the arrow b. It is led into the exchanger by an entry tube 4, then, after flowing over the outer surface 5 of the tubes 2, moving transversely across the baflies constituting the partitions 6, it comes out again through an evacuation tube 7.

According to the invention, an auxiliary liquid is mixed with the gaseous stream circulating in the bundle of tubes 2, without the said liquid vaporising under the temperature and pressure conditions obtained in the exchanger. To this end, e.g. the following arrangements are made: the auxiliary liquid, drawn from a reservoir 8 by means of an adjustable delivery pump 9, is sent through a pipe 10 following the path of the arrow 0, into a chamber 11 arranged between two plates such as 12 arranged in the upper part of the exchanger. On a level with this chamber, each of the tubes 2 is provided with a series of injection elements 13, made up, for example, of simple narrow holes or orifices, through which droplets of the auxiliary liquid pass to mix with the gaseous stream circulating inside the tubes. At the exit from the bundle, the auxiliary liquid-gas mixture passes tangentially into a cyclone type separator 14, where, whilst the gas is evacuated through the pipe 3, the liquid is sent to the reservoir 8 by a pipe 15.

In the preceding example, it has been assumed that the entry of the auxiliary liquid into the circuit through which the gaseous stream flows is made through simple holes whose diameter is prefectly calibrated. It will be appreciated that it is possible to make any other more greatly improved arrangement designed to assist the formation of a liquid film on the internal wall of the tubes, for example, by using entry tubes 13 disposed obliquely with relation to the axis of the tubes 2, as shown in FIG. 2, making it possible to give the liquid, as it is injected, a certain gynation on the wall of the tubes, or (which is simpler), a diaphragm designed to obtain a throttling of the fluid and a suitable pulverisation of it into a spray or droplets mixing with the gas.

Furthermore, the invention is not limited to the foregoing case, in which the exchanger has a straight bundle of tubes. Indeed it is possible to design the tubes in any other shape: hair-pin tubes, coiled tubes, etc. connected to liquid-gas separators of any known type. Lastly, the choice of the auxiliary liquid is determined solely as a function of the working conditions of the exchanger, and,

of course, as 'a function of the chemical and physical of an auxiliary liquid, which will not vaporize at the temperature of said hot gaseous fluid, into said stream of hot gaseous fluid adjacent the inlet end of said tubular heat exchanger, said droplets mixing with said stream of hot gaseous fluid and forming a film of said auxiliary liquid on the internal Wall of said tubular heat exchanger; circulating said cooling fluid in contact with the external wall of said tubular heat exchanger for cooling said hot gaseous fluid and said film of auxiliary liquid; and separating said gaseous fluid from said auxiliary liquid at the outlet from said tubular heat exchanger.

2. A process as defined in claim 1 in which said cooling fluid is circulated in contact with the external wall of said tubular heat exchanger in a direction countercurrent to the direction of flow of said hot gaseous fluid and said auxiliary liquid.

3. A process as defined in claim 1 including recirculating said separated auxiliary liquid from said outlet .and reintroducing it as droplets into said hot gaseous fluid adjacent said inlet end.

4. A process as defined in claim 1 wherein said droplets of said auxiliary liquid are of a uniform size and imparting a gyration to said droplets as they are introduced into said hot gaseous fluid.

5. A heat exchanger for improving the transfer of heat from a stream of hot gaseous fluid to a cooling fluid, comprising: a housing having an inlet for said stream of hot gaseous fluid and an outlet; a bundle of heat exchange tubes through which said hot gaseous fluid flows disposed within said housing with the inlet end of said tubes being 7 in open communication with said housing inlet and with iliary liquid, which will not vaporize at the temperature of said hot gaseous fluid, into each of said tubes adjacent the inlet thereof for mixing with said stream of hot gaseous fluid and forming a film on the internal wall of said tubes; and separator means connected with said housing outlet for separating said gaseous fluid from said auxiliary liquid.

6. A heat exchanger as defined in claim 5 wherein said means for introducing said auxiliary liquid in droplets includes uniformly calibrated, injection elements provided in the wall of said tubes adjacent said inlet end thereof for forming said droplets of a uniform size and for imparting to said droplets a gyration as they enter said stream of hot gaseous fluid.

7. A heat exchanger as defined in claim 5 wherein said means for introducing said auxiliary liquid in droplets includes uniformly calibrated injection elements provided in the wall of said tubes adjacent the inlet end thereof for forming said droplets of a uniform size; a variable delivery purnp having an inlet and an outlet; means connecting said pump inlet with said auxiliary liquid in said separator; and means connecting said pump outlet with said injection elements for recirculating said auxiliary liquid through said heat exchanger.

8. A heat-exchanger as claimed in claim 5, wherein the said bundle of tubes is a straight nest.

References Cited by the Examiner UNITED STATES PATENTS 1,861,158 5/1932 Hilger 222 2,183,136 12/1939 Downs 261-128 2,189,173 2/1940 Hebbard et al. 261-153 2,280,633 4/ 1942 Crawford 55'222 2,796,389 6/1957 Spyjker 55459 2,801,708 8/1957 Fisher 55-268 2,983,229 5/1961 Went 261-35 HARRY B. THORNTON, Primary Examiner. RONALD R. WEAVER, Examiner, 

1. A PROCESS FOR IMPROVING THE TRNSFER OF HEAT FROM A HOT GASEOUS FLUID FLOWING THROUGH A TUBULAR HEAT EXCHANGER TO A COOLING FLUID SURROUNDING SAID TUBULAR HEAT EXCHANGER, COMPRISING: FLOWING A STREAM OF SAID HOT GASEOUS FLUID THROUGH SAID TUBULAR HEAT EXCHANGER; INTRODUCING DROPLETS OF AN AUXILIARY LIQUID, WHICH WILL OT VAPORIZE AT THE TENPERATURE OF SAID HOT GASEOUS FLUID, INTO SAID STREAM OF HOT GASEOUS FLUID ADJACENT THE INLET END OF SAID TUBULAR HEAT EXCHANGER, SAID DROPLETS MIXING WITH SAID STREAM OF HOT GASEOUS FLUID AND FORMING A FILM OF SAID AUXILIARY LIQUID ON THE INTERNAL WALL OF SAID TUBULAR HEAT EXCHANGER; CIRCULATING SAID COOLING FLUID IN CONTACT WITH THE EXTERNAL WALL OF SAID TUBULAR HEAT EXCHANGER FOR COOLING SAID HOT GASEOUS FLUID AND SAID FILM OF AUXILIARY LIQUID; AND SEPARATING SAID GASEOUS FLUID FROM SAID AUXILIARY LIQUID AT THE OUTLET FROM SAID TUBULAR HEAT EXCHANGER. 